1. Field of the Invention
The present invention relates to a semiconductor wafer having an ID mark on the periphery thereof and a method of manufacturing such a semiconductor wafer. The present invention also relates to an equipment for and a method of manufacturing semiconductor device from such a semiconductor wafer.
2. Description of the Related Art
Semiconductor device manufacturing involves several hundreds of processes each of which needs different conditions that must be strictly managed. Management of the process conditions of wafers employs markings made on the wafers. These markings consist of, for example, numerals, characters, and bar codes.
A marking on a semiconductor wafer is used to identify the wafer and indicates, for example, the manufacturing history of the wafer. The marking may be a soft marking made on the surface of the wafer, or a hard marking made on the back of the wafer. The marking is composed of dots made by locally ablating the wafer with laser beam pulses.
The marking is formed in a limited area on a wafer so that it does not interfere with products formed on the wafer. The marking must be visible to workers, and therefore, usually extends from several millimeters to several centimeters causing relatively large space loss on the wafer.
The marking is formed by partly melting a wafer with a laser beam of large energy. A large energy laser beam scatters molten silicon particles around the marking, and the scattered particles spoil semiconductor device formed on the wafer.
When the marking are formed on the surface of a wafer, the marking may disappear or become unrecognizable due to repetitive deposition and chemical mechanical polishing (CMP) processes carried out on the wafer. When the marking are formed on the back of a wafer, irregularities in the marking may cause focal errors in a lithography process and will impose the additional work of reversing the wafer in order to see the marking.
To solve these problems, Japanese Patent Laid Open Publications 08-276284 disclose a technique of making a fine marking on a bevel contour formed along the periphery of a wafer. One of the related arts prepares a liquid crystal marking and passes a laser beam through the liquid crystal marking and an optical system, to form an image of the marking on a bevel contour of a wafer. The laser beam used here has moderate energy, causing no ablation or silicon particle scattering.
The related arts, however, also have problems. Even if wafers are individually provided with markings, the wafers are usually grouped into batches and are processed collectively batch by batch. Each batch includes, for example, 25 wafers. Wafer processing conditions are set for a batch not for individual wafers. The wafers in a batch are collectively handled and managed to have the same manufacturing history. Processing conditions set for a batch of wafers are determined to cover individual variations among the wafers.
As a result, the processing conditions set for a batch of wafers involve redundancies such as a too long process time, deteriorating productivity and increasing costs.
Markings on semiconductor wafers are managed batch by batch by a host computer. Through communication with the host computer, data such as products to be formed on wafers, manufacturing processes and conditions applied to the wafers, and measurements related to the wafers are handled. Communication with the host computer takes a long time, and to save time, only the processing conditions applied to each batch are usually communicated. It is difficult for the related arts to utilize, for example, film thicknesses measured on individual wafers to determine processing conditions applied to the wafers in the next manufacturing process.